Entry 7:Absorption and Transport of Nutrients

I have found a good website explaining the absorption and transport of nutrients today and hence decided to post an entry on this topic, which is also linked to the intesting topic of Digestion!

Most digested molecules of food, as well as water and minerals, are absorbed through the small intestine. The mucosa of the small intestine contains many folds that are covered with tiny fingerlike projections called villi. In turn, the villi are covered with microscopic projections called microvilli. These structures create a vast surface area through which nutrients can be absorbed. Specialized cells allow absorbed materials to cross the mucosa into the blood, where they are carried off in the bloodstream to other parts of the body for storage or further chemical change. This part of the process varies with different types of nutrients.

1)Carbohydrates. The Dietary Guidelines for Americans 2005 recommend that 45 to 65 percent of total daily calories be from carbohydrates. Foods rich in carbohydrates include bread, potatoes, dried peas and beans, rice, pasta, fruits, and vegetables. Many of these foods contain both starch and fiber.

The digestible carbohydrates—starch and sugar—are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine. Starch is digested in two steps. First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose. Then an enzyme in the lining of the small intestine splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body.

Sugars are digested in one step. An enzyme in the lining of the small intestine digests sucrose, also known as table sugar, into glucose and fructose, which are absorbed through the intestine into the blood. Milk contains another type of sugar, lactose, which is changed into absorbable molecules by another enzyme in the intestinal lining.

Fiber is undigestible and moves through the digestive tract without being broken down by enzymes. Many foods contain both soluble and insoluble fiber. Soluble fiber dissolves easily in water and takes on a soft, gel-like texture in the intestines. Insoluble fiber, on the other hand, passes essentially unchanged through the intestines.

2)Proteins. Foods such as meat, eggs, and beans consist of giant molecules of protein that must be digested by enzymes before they can be used to build and repair body tissues. An enzyme in the juice of the stomach starts the digestion of swallowed protein. Then in the small intestine, several enzymes from the pancreatic juice and the lining of the intestine complete the breakdown of huge protein molecules into small molecules called amino acids. These small molecules can be absorbed through the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells.

3)Fats. Fat molecules are a rich source of energy for the body. The first step in digestion of a fat such as butter is to dissolve it into the watery content of the intestine. The bile acids produced by the liver dissolve fat into tiny droplets and allow pancreatic and intestinal enzymes to break the large fat molecules into smaller ones. Some of these small molecules are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules move into the cells of the mucosa. In these cells the small molecules are formed back into large ones, most of which pass into vessels called lymphatics near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.

4)Vitamins. Another vital part of food that is absorbed through the small intestine are vitamins. The two types of vitamins are classified by the fluid in which they can be dissolved: water-soluble vitamins (all the B vitamins and vitamin C) and fat-soluble vitamins (vitamins A, D, E, and K). Fat-soluble vitamins are stored in the liver and fatty tissue of the body, whereas water-soluble vitamins are not easily stored and excess amounts are flushed out in the urine.

5)Water and salt. Most of the material absorbed through the small intestine is water in which salt is dissolved. The salt and water come from the food and liquid you swallow and the juices secreted by the many digestive glands.

Information obtained from:

http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/

Entry 6:Liver, Gallbladder and Pancreas

I have completed most of the stages in digestion and I would like to continue this topic with some further research on the liver, gallbladder and pancreas.
The liver (located under the rib cage in the right upper part of the abdomen), the gallbladder (hidden just below the liver), and the pancreas (beneath the stomach) are not part of the alimentary canal, but these organs are essential to digestion. The liver produces bile, which helps the body absorb fat. Bile is stored in the gallbladder until it is needed. The pancreas produces enzymes that help digest proteins, fats, and carbohydrates. It also makes a substance that neutralizes stomach acid. These enzymes and bile travel through special channels (called ducts) directly into the small intestine, where they help to break down food. The liver also plays a major role in the handling and processing of nutrients, which are carried to the liver in the blood from the small intestine.

Production of digestive juices
The digestive glands that act first are in the mouth—the salivary glands. Saliva produced by these glands contains an enzyme that begins to digest the starch from food into smaller molecules. An enzyme is a substance that speeds up chemical reactions in the body.

The next set of digestive glands is in the stomach lining. They produce stomach acid and an enzyme that digests protein. A thick mucus layer coats the mucosa and helps keep the acidic digestive juice from dissolving the tissue of the stomach itself. In most people, the stomach mucosa is able to resist the juice, although food and other tissues of the body cannot.

After the stomach empties the food and juice mixture into the small intestine, the juices of two other digestive organs mix with the food. One of these organs, the pancreas, produces a juice that contains a wide array of enzymes to break down the carbohydrate, fat, and protein in food. Other enzymes that are active in the process come from glands in the wall of the intestine.

The second organ, the liver, produces yet another digestive juice—bile. Bile is stored between meals in the gallbladder. At mealtime, it is squeezed out of the gallbladder, through the bile ducts, and into the intestine to mix with the fat in food. The bile acids dissolve fat into the watery contents of the intestine, much like detergents that dissolve grease from a frying pan. After fat is dissolved, it is digested by enzymes from the pancreas and the lining of the intestine.

Information obtained from:

1)http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/

2)http://kidshealth.org/parent/general/body_basics/digestive.html

Entry 5:Large Intestine

The next part on my research is on the large intestine. Food continues it's journey from the small intestine to the large intestine. The large intestine is the last attraction in digestive tube and the location of the terminal phases of digestion. In comparison to other regions of the tube, there are huge differences among species in the relative size and complexity of the large intestine. From the small intestine, undigested food (and some water) travels to the large intestine through a muscular ring or valve that prevents food from returning to the small intestine. By the time food reaches the large intestine, the work of absorbing nutrients is nearly finished. The large intestine's main function is to remove water from the undigested matter and form solid waste that can be excreted. Material in the large intestine is mostly indigestible residue and liquid. Movements are due to involuntary contractions that shuffle contents back and forth and propulsive contractions that move material through the large intestine. The large intestine is made up of these three parts:

1. The cecum is a pouch at the beginning of the large intestine that joins the small intestine to the large intestine. This transition area expands in diameter, allowing food to travel from the small intestine to the large. The appendix, a small, hollow, finger-like pouch, hangs at the end of the cecum. Doctors believe the appendix is left over from a previous time in human evolution. It no longer appears to be useful to the digestive process.
2. The colon extends from the cecum up the right side of the abdomen, across the upper abdomen, and then down the left side of the abdomen, finally connecting to the rectum. The colon has three parts: the ascending colon; the transverse colon, which absorb fluids and salts; and the descending colon, which holds the resulting waste. Bacteria in the colon help to digest the remaining food products.
3. The rectum is where feces are stored until they leave the digestive system through the anus as a bowel movement.
   

The appendix is a small projection emerging from the caecum. In human beings, the appendix has no known function and is thought to be a remnant from a previous time in human evolution. In some people, the appendix becomes infected or inflammed(appendicitis) and the appendix will need to be removed via surgery.

Information obtained from:
1)http://www.vivo.colostate.edu/hbooks/pathphys/digestion/largegut/index.html
2)http://kidshealth.org/parent/general/body_basics/digestive.html
3)http://www.gesa.org.au/digestive-system/large_intestine.cfm
4)http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookDIGEST.html#Stages%20in%20the%20Digestive%20Process

Entry 4:The Small Intestine

This is my 4th entry on the Digestive System.I have posted quite a number of posts today as I am lagging in a few entries...I shall continue in the journey of food in the digestive tract.
The small intestine (also known as the small bowel) is the longest portion of the digestive tract - it is more than 6 meters long and is located within the middle of the abdomen. It has three sections, the duodenum, jejunum and ileum. Much of the small intestine is coiled and suspended in a thin layer of fat - which gives the intestine a lot of flexibility and mobility. Most substances in the food we eat need further digestion and must travel into the intestine before being absorbed. When it's empty, an adult's stomach has a volume of one fifth of a cup (1.6 fluid ounces), but it can expand to hold more than 8 cups (64 fluid ounces) of food after a large meal. By the time food is ready to leave the stomach, it has been processed into a thick liquid called chyme. A walnut-sized muscular valve at the outlet of the stomach called the pylorus keeps chyme in the stomach until it reaches the right consistency to pass into the small intestine. Chyme is then squirted down into the small intestine, where digestion of food continues so the body can absorb the nutrients into the bloodstream. Digestion of fats, proteins and carbohydrates contained in the foods you consume, is completed within the small intestine. The resulting nutrients produced are absorbed through the lining of the small intestine and transferred to the bloodstream. The small intestine is the site where most of the nutrients from ingested food are absorbed and is covered in wrinkles or folds called plicae circulares. The purpose of these wrinkles and projections is to increase surface area for absorption of nutrients. From the small intestine, undigested food (and some water) travels to the large intestine through a muscular ring or valve that prevents food from returning to the small intestine.

Information obtained from:
1)http://kidshealth.org/parent/general/body_basics/digestive.html
2)http://www.gesa.org.au/digestive-system/small_intestine.cfm
3)http://en.wikipedia.org/wiki/Small_intestine

Entry 3:The Stomach

I have learnt much more about the stomach today! At the beginning of today's research, I thought the stomach was just a muscular bag! However, now I do know the stomach is more than that. The stomach is an organ of digestion.The main function of the stomach is to process and transport food. After feeding, the contractile activity of the stomach helps to mix, grind and eventually evacuate small portions of chyme into the small bowel, while the rest of the chyme is mixed and ground. It has a saclike shape and is located between the esophagus and the intestines. Almost every animal has a stomach.The stomach muscles churn and mix the food with acids and enzymes, breaking it into much smaller, digestible pieces. An acidic environment is needed for the digestion that takes place in the stomach. Glands in the stomach lining produce about 3 quarts (2.8 liters) of these digestive juices each day. The lining of the stomach contains glands, which make and release (secrete) the stomach juices. The stomach juices contain an acid and a digestive enzyme called pepsin. These begin to flow as soon as we see or smell food, well before food even enters the stomach. The enzyme starts to break down (digest) proteins in the food so that the body can absorb them. The acid is necessary for the enzyme to work properly. It also helps to kill bacteria that might be in the food and so helps to protect against food poisoning.
There are other glands in the stomach lining that make thick mucus. This mucus helps to protect the stomach lining from being damaged by the acid and protein-digesting enzyme in the stomach juices. After about two hours in the stomach, the semi-liquid, partly digested food moves into the duodenum where it continues to be digested. The digested food then moves through the small intestine (small bowel) where the digested nutrients are absorbed into the body. The waste that is left behind then moves through to the large bowel where water is absorbed so that the waste matter begins to solidify into the faeces or stool.

Information obatained from: 1)http://kidshealth.org/parent/general/body_basics/digestive.html
2)http://www.mamashealth.com/organs/stomach.asp
3)http://www.enel.ucalgary.ca/People/Mintchev/stomach.htm
4)http://www.cancerhelp.org.uk/help/default.asp?page=3905

Entry 2:The Oesophagus

I have decided to continue on my research on the Digestive System today and I started on swallowing and the Oesophagus! Swallowing, which is accomplished by muscle movements in the tongue and mouth, moves the food into the throat, or the pharynx. The pharynx, a passageway for food and air, is about 5 inches (12.7 centimeters) long. A flexible flap of tissue called the epiglottis reflexively closes over the windpipe when we swallow to prevent choking.The oesophagus(British spelling), which is sometimes known as the gullet, is an organ found in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. It is usually around 25 to 30 cm long, connecting the mouth to the stomach. Food is passed through the oesophagus by using the process of peristalsis. Specifically, it contains the pharynx, which is the body cavity that is common to the digestive factory and respiratory system with the stomach, where the second stage of digestion is initiated. The oesophagus is lined with mucuos membrane, and is more deeply lined with muscle that acts with peristaltic action to move swallowed food down to the stomach. A person normally isn't aware of the movements of the esophagus, stomach, and intestine that take place as food passes through the digestive tract. At the end of the esophagus, a muscular ring or valve called a spincter allows food to enter the stomach and then squeezes shut to keep food or fluid from flowing back up into the oesophagus.

Information obtained from:1)http://en.wikipedia.org/wiki/Oesophagus
2)http://kidshealth.org/parent/general/body_basics/digestive.html

Entry 1:Digestion and Salivary Glands

Digestion is the breaking down of food in the body, into a form that can be absorbed and used or excreted. It is also the process by which the body breaks down food into smaller components that can be absorbed by the blood stream.The digestive system is made up of the digestive tract,which is a series of hollow organs joined in a long, twisting tube from the mouth to the anus,and to other organs that help the body break down and absorb food.Even before you eat, when you smell a tasty food, see it, or think about it, digestion begins.
Part 1:Salivary Glands
The salivary glands are part of the digestive system. They do not function mechanically, but subject to the control of the brain.There are 3 pairs of salivary glands, of which one is in the front ear, one under the tongue, and the last one under the lower jaw. One interesting fact about the largest salivary glands is that it secrates about 23,600 litres of saliva in a lifetime!Each salivary gland has a special job too. The parotid gland, which is also the largest one, secretes large quantities of watery saliva.The main purpose of this saliva is to dilute and to moisten the food well.Which of the salivary glands will produce the most saliva also depends on the food we take in. Lower glands will function when we are chewing on food which do not need to be moistened, and the parotid gland goes to work and produce large quantities of watery saliva for dry food. When the food is ready to be swallowed, the tongue then pushes a tiny bit of food called a bolus toward the back of your throat into the opening of the esophagus, the second part of the digestive tract. I shall continue on this in my next entry.

Information obtained from:1)http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/
2)http://en.wikipedia.org/wiki/Digestive_system
3)Encyclopedia:Tell Me Why
4)http://kidshealth.org/kid/htbw/digestive_system.html